1. Field of the Invention
The present invention concerns the deposition of fluorine modified, titanium dioxide films (TiO.sub.2) onto hot glass by atmospheric pressure chemical vapor deposition (APCVD) using TiCl.sub.4 vapor. The invention is also suitable for depositing other metallic oxide films from their metallic halides such as SnCl.sub.4, GeCl.sub.4, and VCl.sub.4.
2. Technical Advance
Beneficial metallic oxide coatings for glass are known for improving one or more properties of the glass. Commercial glass coaters desire metallic oxide coatings that are free of contaminants or surface irregularities that diminish the optical properties of the glass. To be economical, the coatings must be deposited at rates that are commensurate with the operating speeds of a commercial float glass line. An economical process also requires that the chemical components be readily available and inexpensive. Materials that fulfill these needs are often metal chlorides. However, when metal chlorides are deposited at fast rates the resultant films often have rough surfaces which scatter the impinging light, causing haze. This haze reduces optical transmission and gives the article an aesthetically unpleasing look. This invention is a Atmospheric Pressure Chemical Vapor Deposition (APCVD) method for depositing films of metal oxides at very fast rates which have a low degree of haze using readily available, inexpensive, metal halide precursors.
Prior art processes generally have utilized Solution Spray, Low Pressure CVD, or Atmospheric Pressure CVD (APCVD). Solution sprays often require solvents and produce poor quality films while low pressure CVD techniques are batch operations and produce films at low deposition rates. Films that have been deposited by APCVD techniques are often hazy and frequently require thermal post-treatments to obtain the desired properties, and more expensive starting materials are often used. In contrast, the method of the present invention allows one to use inexpensive metal halides in a continuous APCVD process to produce oxide films at rates .gtoreq.900 .ANG./sec. These films have haze values of &lt;1% and are uniform and continuous with reduced surface roughness.
The method of the present invention enables glass coaters to deposit high quality TiO.sub.2 films on the float line at the high line speeds practiced with commercial float lines without any major disruption to the existing coating set-up.